|If the drive is not showing in Disk Management then look in Device Manager to see if it is there.|
You may have installed the drive into the enclosure wrong. Most times the jumper position is the problem. Depending on the brand of drive you may need to set as Master, Master alone or leave all jumpers off.
Is the drive a 2.5" or 3.5"?
Is the drive new, used? What is the history of this drive?